If you can slow roll (ie use both rudder and elevator to keep it straight) you can learn how to do a rolling loop, it is just a matter of using more throws to get you to go around the loop, the timing is the same.

As with most things, it just takes practice. I can do them, but they are very messy at the moment, and I still duck out 50% of the time on the down leg (up I'm fine with now).